Mechanical Ventricular Pacing Non-Capture Detection for a Refractory Period Stimulation (RPS) Pacing Therapy Using at Least One Lead-Based Accelerometer

ABSTRACT

A system and method for monitoring at least one chamber of a heart (e.g., a left ventricular chamber) during delivery of a refractory period stimulation (RPS) therapy to determine if the desired non-capture (i.e., lack of ventricular mechanical capture due to refractory period stimulation) occurs. The system includes an implantable or external cardiac stimulation device in association with a set of leads such as epicardial, endocardial, and/or coronary sinus leads equipped with motion sensor(s). The device receives and processes acceleration sensor signals to determine a signal characteristic indicative of chamber capture due to pacing stimulus delivery, non-capture due to RPS therapy delivery, and/or contractile status based on the qualities of evoked response to pacing stimulation.

STATEMENT OF INCORPORATION BY REFERENCE

The present disclosure incorporates U.S. Pat. No. 7,142,929 entitled,“RECONFIGURABLE, FAULT TOLERANT MULTIPLE-ELECTRODE CARDIAC LEAD SYSTEMS”and U.S. Pat. No. 7,142,916 entitled, “CARDIAC PACING MODALITY HAVINGIMPROVED BLANKING, TIMING, AND THERAPY DELIVERY METHODS FOREXTRASYSTOLIC STIMULATION PACING THERAPY” as if fully set forth herein.

FIELD OF THE INVENTION

The present invention relates generally to implantable medical devicesfor monitoring or treating cardiac dysfunction by altering mechanicalcontractile function, and more particularly to devices and methods thatrequire optimization of more than one electrical pulse for evoking thedesired mechanical response during ventricular pacing, whether suchpacing involves ventricles (i.e., bi-ventricular) or a single chamberdelivery or combinations thereof (e.g., pacing pulses betweenventricular configurations for contractility modulation, refractoryperiod stimulation, stroke volume augmentation and the like).

BACKGROUND OF THE INVENTION

Determination of ventricular pacing capture thresholds is important inorder to ensure that a patient is receiving a desired pacing therapy orfor configuring the resulting mechanical ventricular contraction to oneor more sequentially delivered pacing of various amplitudes andsequences. During the delivery of sub-threshold capture pulses orrefractory period pulses to augment mechanical contraction, it isimportant to establish that such sub-threshold or refractory pulses donot by themselves result in a separate mechanical ventricularcontraction, but results instead in the mechanical augmentation of thecontraction initiated by the capturing pacing pulse. At least one basedaccelerometer is used to determine the relevant pacing parametersincluding the upper threshold, shortest interval(s), waveform, or timingrelative to another cardiac event, in order that the clinician is ableto set a range of electrical pulses that does not cause separatemechanical ventricular contractions with each electrical stimulus.Additionally, a range of parameters can be determined in order tooptimally augment each ventricular contraction using the minimal amountof energy. The configuration of the electrical pulses may therefore bewithin a specified range as required to minimize the device energyrequired while ensuring that the desired therapy is maintained. Ineither case an algorithm can be incorporated in the device and/orprogrammer to use a motion sensor to measure the mechanical effects ofone or more ventricular pacing pulses from either the left or rightventricular chamber in order to optimize the net mechanical ventriculareffect by determining the range of parameters for electrical stimulationthat results in a within a range of non-capturing electrical pacingpulse(s).

During normal cardiac function, the atria and ventricles observeconsistent time-dependent relationships during the systolic(contractile) phase and the diastolic (relaxation) phase of the cardiaccycle. During cardiac dysfunction associated with pathologicalconditions or following cardiac-related surgical procedures, thesetime-dependent mechanical relationships are often altered. Thisalteration, when combined with the effects of weakened cardiac muscles,reduces the ability of the ventricle to generate contractile strengthresulting in hemodynamic insufficiency.

Ventricular dyssynchrony following coronary artery bypass graft (CABG)surgery is a problem encountered relatively often, requiringpost-operative temporary pacing. Atrio-biventricular pacing has beenfound to improve post-operative hemodynamics following such procedures.

Cardiac pacing may be applied to one or both ventricles or multipleheart chambers, including one or both atria, to improve cardiac chambercoordination, which in turn is thought to improve cardiac output andpumping efficiency. Clinical follow-up of patients pacing therapy hasshown improvements in hemodynamic measures of cardiac function,ventricular volumes, and wall motion.

Implantable sensors for monitoring heart wall motion have been describedor implemented for use in relation to the right ventricle. A sensorimplanted in the heart mass for monitoring heart function by monitoringthe momentum or velocity of the heart mass is generally disclosed inU.S. Pat. No. 5,454,838 issued to Vallana et al. A catheter forinsertion into the ventricle for monitoring cardiac contractility havingan acceleration transducer at or proximate the catheter tip is generallydisclosed in U.S. Pat. No. 6,077,236 issued to Cunningham. Implantableleads incorporating accelerometer-based cardiac wall motion sensors aregenerally disclosed in U.S. Pat. No. 5,628,777 issued to Moberg, et al.A device for sensing natural heart acceleration is generally disclosedin U.S. Pat. No. 5,693,075, issued to Plicchi, et al. A system formyocardial tensiometery including a tensiometric element disposed at alocation subject to bending due to cardiac contractions is generallydisclosed in U.S. Pat. No. 5,261,418 issued to Ferek-Petric et al. Allof the above-cited patents are hereby incorporated herein by referencein their entirety.

It is apparent from the above discussion that a need remains forproviding a device and method for monitoring the mechanical effects ofdelivering one or more electrical pulses to the heart to ensure that apatient is in fact receiving a desired therapy.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for monitoringmechanical pacing capture, by determining the bounds of pacing pulseparameters including amplitude, waveform, width, polarity, inter andintraventricular sequence and the like, for determining that the pulsethat results in an augmentation of mechanical contraction of an originalcapturing electrical pulse, and does not instead initiate one or moreseparate ventricular contractions. In one embodiment, the presentinvention is realized in a pacing delivery system that includes animplantable multi-chamber pulse generator and associated lead systemwherein a LV coronary sinus lead or left ventricular epicardial lead isprovided with a sensor for detecting acceleration of the LV free wall orportions thereof, also referred to herein as “lateral wall” of the LV.In an alternative embodiment, a temporary, external pulse generator iscoupled to temporary pacing leads including a temporary LV pacing leadis equipped with a motion sensor (e.g., an accelerometer).

In one form, a therapy known as refractory period stimulation (RPS)therapy one (or more) pacing pulses are delivered within (i.e., during)the refractory period of a cardiac chamber. Thus these pulses are notintended to mechanically capture the chamber and thus not result in anevoked response but enhance mechanical contractility on subsequentcardiac cycles. That is, the non-capturing RPS therapy providesaugmented volume and flow from the chamber on successive cardiac cycles,versus causing separate ventricular contractions due to stimulationpulse delivery. RPS therapy delivery thus provides benefits for heartfailure patients having diminished cardiac performance (i.e., cardiacinsufficiency) and it has also been shown to improve cardiac perfusionfollowing cardiac resuscitation therapy delivery (e.g., defibrillation).

According to the invention, during a temporal window following amechanically- and/or electrically-sensed cardiac event (e.g.,ventricular contraction) and while the RPS therapy delivery is occurringsignals from the motion sensor are monitored to determine if theintended lack of mechanical capture event is detected for a givencardiac cycle. If not, the RPS therapy delivery parameters can beadjusted, a mode switch can occur to a different pacing mode, or the RPStherapy delivery can be terminated.

While the examples and depictions of the instant invention primarilyinvolve placement of motion sensor(s) in, about, and around the LV, theinvention should not be considered as so limited. In fact, the motionsensors can operate globally (e.g., disposed intermediate the atria andventricles) or locally (e.g., disposed in, on, or about the rightventricle or one of the atrial chambers).

In one embodiment, the sensor comprises an accelerometer, which may be auniaxial, biaxial, or triaxial accelerometer. Other types of sensorscapable of generating a signal proportional to LV lateral wallacceleration can be utilized (e.g., tensiometric, pressure sensors andthe like). The sensor can be disposed in or proximate the mid- ormid-basal LV free wall segments.

The implantable or external system receives and processes theacceleration sensor signal to determine whether mechanical pacingcapture is actually occurring. Signal processing is performed to monitorand/or measure any acceleration signal(s) during a period of timefollowing delivery of the RPS therapy. Various metrics related tocapture can be stored with other parametric or physiologic data formonitoring and/or diagnostic purposes via telemetry to local or remoteclinicians.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A depicts an exemplary implantable, multi-chamber cardiacpacemaker in which the present invention may be implemented.

FIG. 1B depicts an exemplary implantable, multi-chamber cardiacpacemaker coupled to a patient's heart via transvenous endocardial leadsand an additional left ventricular epicardial lead equipped withacceleration sensor.

FIG. 2 is a schematic block diagram of an exemplary multi-chamberimplantable pulse generator that provides delivery of a RPS therapy andis capable of processing left ventricular acceleration signal input.

FIG. 3 depicts an alternative, epicardial lead system coupled to apatient's heart.

FIG. 4 is a flow chart providing an overview of a method for monitoringLV non-capture based on sensing LV lateral wall acceleration.

FIG. 5 is a plot of sample LV lateral wall acceleration data andsimultaneous hemodynamic and electrical data acquired during one cardiaccycle wherein a first depolarization (P1) is followed by delivery of atleast one second pacing stimulus (P2) delivered during the refractoryperiod.

FIG. 6 is a flow chart summarizing steps included in a method forconfirming that no evoked response occurs due to delivery of RPS therapybased on left ventricular lateral wall acceleration signal collectedsubsequent to stimulus—denoted as a P2 pulse herein.

FIG. 7 a flow chart summarizing steps included in a method fordetermining non-capture of the LV due to RPS therapy delivery based onleft ventricular acceleration.

DETAILED DESCRIPTION OF THE INVENTION

As indicated above, the present invention is directed toward providing amethod and apparatus for monitoring one of more chambers of a heart foroptimizing electrical pulses using mechanical parameters based onmonitoring ventricular wall acceleration (e.g., LV free wall). Inparticular, the present invention is useful for ensuring non-capture ofone or more chambers of a heart during RPS therapy delivery to treatheart failure. The present invention is also useful in ensuringnon-capture during temporary pacing applied for treating post-operativeventricular dyssynchrony. As such, the present invention may be embodiedin an implantable cardiac pacing system including a dual chamber ormultichamber pacemaker and associated set of leads. Alternatively, thepresent invention may be embodied in a temporary pacing system includingan external pacing device with associated temporary pacing leads.

FIG. 1A depicts an exemplary implantable, multi-chamber cardiacpacemaker 14 in which the present invention may be implemented. Themulti-chamber pacemaker 14 is provided for restoring ventricularsynchrony by delivering pacing pulses to one or more heart chambers asneeded to control the heart activation sequence. The pacemaker 14 isshown in communication with a patient's heart 10 by way of three leads16,32,52. The heart 10 is shown in a partially cut-away viewillustrating the upper heart chambers, the right atrium (RA) and leftatrium (LA), and the lower heart chambers, the right ventricle (RV) andLV, and the coronary sinus (CS) extending from the opening in the RAlaterally around the atria to form the great cardiac vein 48, whichbranches to form inferior cardiac veins.

The pacemaker 14, also referred to herein as the “implantable pulsegenerator” or “IPG,” is implanted subcutaneously in a patient's bodybetween the skin and the ribs. Three transvenous endocardial leads16,32,52 connect the IPG 14 with the RA, the RV and the LV,respectively. Each lead has at least one electrical conductor andpace/sense electrode. A remote indifferent can electrode 20 is formed aspart of the outer surface of the housing of the IPG 14. The pace/senseelectrodes and the remote indifferent can electrode 20 can beselectively employed to provide a number of unipolar and bipolarpace/sense electrode combinations for pacing and sensing functions.

The depicted bipolar endocardial RA lead 16 is passed through a veininto the RA chamber of the heart 10, and the distal end of the RA lead16 is attached to the RA wall by an attachment mechanism 17. The bipolarendocardial RA lead 16 is formed with an in-line connector 13 fittinginto a bipolar bore of IPG connector block 12 that is coupled to a pairof electrically insulated conductors within lead body 15 and connectedwith distal tip RA pace/sense electrode 19 and proximal ring RApace/sense electrode 21 provided for achieving RA pacing and sensing ofRA electrogram (EGM) signals.

Bipolar, endocardial RV lead 32 is passed through the RA into the RVwhere its distal ring and tip RV pace/sense electrodes 38,40 are fixedin place in the apex by a conventional distal attachment mechanism 41.The RV lead 32 is formed with an in-line connector 34 fitting into abipolar bore of IPG connector block 12 that is coupled to a pair ofelectrically insulated conductors within lead body 36 and connected withdistal tip RV pace/sense electrode 40 and proximal ring RV pace/senseelectrode 38 provided for RV pacing and sensing of RV EGM signals. RVlead 32 may optionally include a RV wall motion sensor 60. RV wallmotion sensor 60 may be positioned into or proximate the RV apex fordetecting motion or acceleration of the RV apical region. Implantationof an acceleration sensor in the right ventricle is generally disclosedin the above-cited U.S. Pat. No. 5,693,075 issued to Plicchi, et al.

In this illustrated embodiment, a unipolar, endocardial LV CS lead 52 ispassed through the RA, into the CS and further into a cardiac vein toextend the distal LV CS pace/sense electrode 50 alongside the LV chamberto achieve LV pacing and sensing of LV EGM signals. The LV CS lead 52 iscoupled at the proximal end connector 54 fitting into a bore of IPGconnector block 12. A small diameter unipolar lead body 56 is selectedin order to lodge the distal LV CS pace/sense electrode 50 deeply in acardiac vein branching from the great cardiac vein 48.

In accordance with the present invention, the coronary sinus lead 52 isprovided with a sensor 62 capable of generating a signal proportional tothe acceleration of the left ventricular free wall. Sensor 62 ispreferably embodied as a uniaxial, biaxial, or triaxial accelerometercontained in a capsule of a relatively small size and diameter such thatit may be included in a coronary sinus lead without substantiallyincreasing the lead diameter or impairing the ability to steer the leadto a left ventricular pacing and sensing site. Radial acceleration maynot be as valuable in assessing LV wall acceleration and optimizingpacing intervals as longitudinal acceleration, therefore, a uniaxialaccelerometer may be adequate for these purposes. Sensor 62 mayalternatively be provided as another type of sensor such as an optical,acoustical sensor or a sensor having piezoelectric, inductive,capacitive, resistive, or other elements which produce a variable signalproportional to left ventricular acceleration or from which variationsin LV acceleration can be derived. Sensor 62 is preferably located on CSlead 52 such that when CS lead 52 is positioned for LV pacing andsensing, sensor 62 is located approximately over the LV free wallmid-lateral to mid-basal segments. The depicted positions of the leadsand electrodes shown in FIG. 1A in or about the right and left heartchambers are approximate and merely exemplary. For example, an LVacceleration sensor 62 may alternatively be located on CS lead 52 suchthat sensor 62 is positioned in the coronary sinus, in the great cardiacvein, or in any accessible inferior cardiac vein. Furthermore, it isrecognized that alternative leads and pace/sense electrodes that areadapted for placement at pacing or sensing sites on or in or relative tothe RA, LA, RV and LV may be used in conjunction with the presentinvention.

In a four chamber embodiment, LV CS lead 52 could bear a proximal LA CSpace/sense electrode positioned along the lead body to lie in the largerdiameter coronary sinus adjacent the LA for use in pacing the LA orsensing LA EGM signals. In that case, the lead body 56 would encase aninsulated lead conductor extending proximally from the more proximal LACS pace/sense electrode(s) and terminating in a bipolar connector 54.

FIG. 1B depicts an exemplary implantable, multi-chamber cardiacpacemaker coupled to a patient's heart via transvenous endocardial leadsand an additional left ventricular epicardial lead equipped withacceleration sensor 62. Patients may already be implanted with atransvenous lead system that includes a coronary sinus lead 52 that isnot equipped with an acceleration sensor. Such patients may benefit fromthe placement of an epicardial lead 64 equipped with an accelerationsensor 62 coupled to IPG 14 via a connector 66 so as to provide an LVacceleration signal for use in a closed-loop feedback system forproviding PESP therapy at optimal pacing intervals.

Epicardial lead 64 is provided with a fixation member 63 which may serveadditionally as a pacing and/or sensing electrode. In some cases, anepicardial lead may be preferred over a coronary sinus lead due to thedifficulty in advancing a coronary sinus lead into a relatively smallcardiac vein over the LV free wall. Placement of a coronary sinus leadcan be a cumbersome task due to the tortuosity of the cardiac veins.Therefore, it may be desirable, at least in some patients, to provide anepicardial lead that can be positioned on the LV lateral wall forpacing, EGM sensing and acceleration monitoring, eliminating the needfor a coronary sinus lead. Alternatively, it may be desirable to deploya small diameter coronary sinus lead for LV pacing and EGM sensing witha separate LV epicardial lead positioned for sensing LV lateral wallacceleration.

The embodiment generally shown in FIG. 1B is particularly advantageousfor use in selecting one or more RPS therapy delivery pacing sites. Withepicardial lead 64 fixed at a desired location for assessing LV lateralwall acceleration, the effect of pacing at different locations in one ormore heart chambers can be evaluated by deploying the transvenous pacingleads 16,32 and 52 to different locations (e.g., to tissue locationsthat remain refractory longer than other locations, such as infractedtissue). In particular, coronary sinus lead 52 may be advanced todifferent locations until one or more such locations are identifiedbased on analysis of the signal from LV acceleration sensor 62. Byproviding acceleration sensor 62 on a separate, epicardial lead 64, theposition of RPS therapy delivery electrode 50, provided on coronarysinus lead 52, may be adjusted independently of sensor 62. If theposition of pacing electrode 50 needs adjusting, acceleration sensor 62may remain fixed at a desired measurement site on the LV lateral wallthereby allowing comparisons to be made between measurements repeated atthe same location for different pacing intervals and/or pacing sites.That is, relatively longer or additional RPS pulses can be deliveredwithout capturing the chamber and presumably increased benefits ofchronic RPS therapy delivery can be realized.

FIG. 2 is a schematic block diagram of an exemplary multi-chamber IPG14, such as that shown in FIG. 1A or 1B, that provides delivery of aPESP therapy and is capable of processing left ventricular accelerationsignal input. The IPG 14 is preferably a microprocessor-based device.Accordingly, microprocessor-based control and timing system 102, whichvaries in sophistication and complexity depending upon the type andfunctional features incorporated therein, controls the functions of IPG14 by executing firmware and programmed software algorithms stored inassociated RAM and ROM. Control and timing system 102 may also include awatchdog circuit, a DMA controller, a block mover/reader, a CRCcalculator, and other specific logic circuitry coupled together byon-chip data bus, address bus, power, clock, and control signal lines inpaths or trees in a manner known in the art. It will also be understoodthat control and timing functions of IPG 14 can be accomplished withdedicated circuit hardware or state machine logic rather than aprogrammed microcomputer.

The IPG 14 includes interface circuitry 104 for receiving signals fromsensors and pace/sense electrodes located at specific sites of thepatient's heart chambers and delivering cardiac pacing to control thepatient's heart rhythm and resynchronize heart chamber activation. Theinterface circuitry 104 therefore includes a therapy delivery system 106intended for delivering cardiac pacing impulses under the control ofcontrol and timing system 102. Delivery of pacing pulses to two or moreheart chambers is controlled in part by the selection of programmablepacing intervals, which can include atrial-atrial (A-A),atrial-ventricular (A-V), and ventricular-ventricular (V-V) intervals.

Physiologic input signal processing circuit 108 is provided forreceiving cardiac electrogram (EGM) signals for determining a patient'sheart rhythm. Physiologic input signal processing circuit 108additionally receives signals from LV wall acceleration sensor 62, andoptionally RV wall motion sensor 60, and processes these signals andprovides signal data to control and timing system 102 for further signalanalysis. For purposes of illustration of the possible uses of theinvention, a set of lead connections are depicted for making electricalconnections between the therapy delivery system 106 and the input signalprocessing circuit 108 and sets of pace/sense electrodes, accelerationsensors, and any other physiological sensors located in operativerelation to the RA, LA, RV and LV.

Control and timing system 102 controls the delivery of bi-atrial,bi-ventricular, or multi-chamber cardiac pacing pulses at selectedintervals intended to improve heart chamber synchrony. The delivery ofpacing pulses by IPG 14 may be provided according to programmable pacingintervals, such as programmable conduction delay window times asgenerally disclosed in U.S. Pat. No. 6,070,101 issued to Struble et al.,incorporated herein by reference in its entirety, or programmablecoupling intervals as generally disclosed in above-cited U.S. Pat. No.6,473,645 issued to Levine. Selection of the programmable pacingintervals is preferably based on a determination of left ventricularlateral wall acceleration derived from sensor 62 signals as will bedescribed in greater detail below.

The therapy delivery system 106 can optionally be configured to includecircuitry for delivering cardioversion/defibrillation therapy inaddition to cardiac pacing pulses for controlling a patient's heartrhythm. Accordingly, leads in communication with the patient's heartcould additionally include high-voltage cardioversion or defibrillationshock electrodes.

A battery 136 provides a source of electrical energy to power componentsand circuitry of IPG 14 and provide electrical stimulation energy fordelivering electrical impulses to the heart. The typical energy sourceis a high energy density, low voltage battery 136 coupled with a powersupply/POR circuit 126 having power-on-reset (POR) capability. The powersupply/POR circuit 126 provides one or more low voltage power (Vlo), thePOR signal, one or more reference voltage (VREF) sources, currentsources, an elective replacement indicator (ERI) signal, and, in thecase of a cardioversion/defibrillator capabilities, high voltage power(Vhi) to the therapy delivery system 106. Not all of the conventionalinterconnections of these voltages and signals are shown in FIG. 2.

Current electronic multi-chamber pacemaker circuitry typically employsclocked CMOS digital logic ICs that require a clock signal CLK providedby a piezoelectric crystal 132 and system clock 122 coupled thereto aswell as discrete components, e.g., inductors, capacitors, transformers,high voltage protection diodes, and the like that are mounted with theICs to one or more substrate or printed circuit board. In FIG. 2, eachCLK signal generated by system clock 122 is routed to all applicableclocked logic via a clock tree. The system clock 122 provides one ormore fixed frequency CLK signal that is independent of the batteryvoltage over an operating battery voltage range for system timing andcontrol functions and in formatting uplink telemetry signaltransmissions in the telemetry I/O circuit 124.

The RAM registers included in microprocessor-based control and timingsystem 102 may be used for storing data compiled from sensed EGMsignals, acceleration signals, and/or relating to device operatinghistory or other sensed physiologic parameters for uplink telemetrytransmission upon receipt of a retrieval or interrogation instructionvia a downlink telemetry transmission. Criteria for triggering datastorage can be programmed via downlinked instructions and parametervalues. Physiologic data, including acceleration data, may be stored ona triggered or periodic basis or by detection logic within thephysiologic input signal processing circuit 108. In some cases, the IPG14 includes a magnetic field sensitive switch 130 that closes inresponse to a magnetic field, and the closure causes a magnetic switchcircuit 120 to issue a switch closed (SC) signal to control and timingsystem 102 which responds in a magnet mode. For example, the patient maybe provided with a magnet 116 that can be applied over thesubcutaneously implanted IPG 14 to close switch 130 and prompt thecontrol and timing system to deliver a therapy and/or store physiologicdata. Event related data, e.g., the date and time and current pacingparameters, may be stored along with the stored physiologic data foruplink telemetry in a later interrogation session.

Uplink and downlink telemetry capabilities are provided to enablecommunication with either a remotely located external medical device ora more proximal medical device on or in the patient's body. Stored EGM,or LV acceleration data as well as real-time generated physiologic dataand non-physiologic data can be transmitted by uplink RF telemetry fromthe IPG 14 to the external programmer or other remote medical device 26in response to a downlink telemetered interrogation command. As such, anantenna 128 is connected to radio frequency (RF) transceiver circuit 124for the purposes of uplink/downlink telemetry operations. Telemeteringboth analog and digital data between antenna 128 and an external device26, also equipped with an antenna 118, may be accomplished usingnumerous types of telemetry systems known in the art for use inimplantable devices.

The physiologic input signal processing circuit 108 includes at leastone electrical signal amplifier circuit for amplifying, processing andin some cases detecting sense events from characteristics of theelectrical sense signal or sensor output signal. The physiologic inputsignal processing circuit 108 may thus include a plurality of cardiacsignal sense channels for sensing and processing cardiac signals fromsense electrodes located in relation to a heart chamber. Each suchchannel typically includes a sense amplifier circuit for detectingspecific cardiac events and an EGM amplifier circuit for providing anEGM signal to the control and timing system 102 for sampling, digitizingand storing or transmitting in an uplink transmission. Atrial andventricular sense amplifiers include signal processing stages fordetecting the occurrence of a P-wave or R-wave, respectively andproviding an atrial sense or ventricular sense event signal to thecontrol and timing system 102. Timing and control system 102 responds inaccordance with its particular operating system to deliver or modify apacing therapy, if appropriate, or to accumulate data for uplinktelemetry transmission in a variety of ways known in the art. Thus theneed for pacing pulse delivery is determined based on EGM signal inputaccording to the particular operating mode in effect. The intervals atwhich pacing pulses are delivered are preferably determined based on anassessment of LV wall acceleration data.

As such, input signal processing circuit 108 further includes signalprocessing circuitry for receiving, amplifying, filtering, averaging,digitizing or otherwise processing the LV wall acceleration sensorsignal. If additional acceleration or other wall motion sensors areincluded in the associated lead system, for example a RV wall motionsensor, additional wall motion signal processing circuitry may beprovided as needed. Acceleration signal processing circuitry is furtherprovided for detection and/or determination of one or more accelerationsignal characteristics such as maximum and minimum peak amplitudes,slopes, integrals, or other time or frequency domain signalcharacteristics that may be used as indices of acceleration.Acceleration data from an LV lateral wall acceleration sensor signal aremade available to control and timing system 102 via LV MOTION signalline for use in algorithms performed for identifying pacing intervalsproducing optimal LV acceleration. If an RV wall motion sensor ispresent, an additional RV MOTION signal line provides RV wall motionsignal data to control and timing system 102.

FIG. 3 depicts an alternative, epicardial lead system coupled to apatient's heart. Epicardial leads may be used in conjunction with eitherchronically implantable or temporary external pacing systems. In theembodiment shown, RV epicardial lead 80 is shown fixed via an activefixation electrode 82 near the apex of the RV such that the activefixation electrode 82 is positioned in contact with the RV epicardialtissue for pacing and sensing in the right ventricle. RV epicardial lead80 may optionally be equipped with an RV wall motion sensor 84 fordetecting motion or acceleration of the RV apical region. LV epicardiallead 70 is shown fixed via an active fixation electrode 72 in the LVfree wall such that active fixation electrode 72 is positioned incontact with the LV epicardial tissue for pacing and sensing in the leftventricle. LV epicardial lead 70 is equipped with an acceleration sensor74 for detecting acceleration of the LV free wall. Epicardial leadsystems may further include epicardial RA and/or LA leads. Variouscombinations of epicardial and transvenous endocardial leads are alsopossible for use with biventricular or multichamber cardiac stimulationsystems.

In FIG. 3, RV and LV epicardial leads 70 and 80 are shown coupled to anexternal, temporary cardiac pacing device 90. External pacing device 90is preferably a microprocessor controlled device includingmicroprocessor 96 with associated RAM and ROM for storing and executingfirmware and programmable software for controlling the delivery ofpacing pulses to LV and RV pace/sense electrodes 72 and 82. Externaldevice 90 receives signals from and delivers electrical pulses to LV andRV pace/sense electrodes 72 and 82 via conductors included in LVepicardial lead body 76 and RV epicardial lead body 86. EGM signals, LVlateral wall acceleration signals, and optionally RV wall motion signalsare received as input to input signal processing circuitry 94. Pacingimpulses are delivered by output circuitry 92 as needed, based on sensedEGM signals, at intervals determined based on signals received from LVacceleration sensor 74 as will be described in greater detail below. Itis recognized that an epicardial lead system such as that shown in FIG.3 that includes an LV acceleration sensor and optionally an RV wallmotion sensor may alternatively be used in conjunction with animplantable pacing system, such as the multi-chamber system describedabove and shown in FIGS. 1A and 2.

External device 90 of FIG. 3 and implantable device 14 of FIGS. 1A, 1Band 2 are shown to provide both sensing/monitoring and pacing deliverycapabilities. Certain device features may be enabled or disabled asdesired. For example, monitoring of LV lateral wall acceleration withoutdelivery of a RPS therapy may be desired. Acceleration sensor signaldata may therefore be received, processed and stored by an implantableor external device for later analysis and review by a clinician as wellas for comparison to improve detection of (un-desired) capture due toRPS therapy delivery. For example, the wall motion from a capturingpulse can be used as a template or for morphological analysis in anattempt to determine whether one or more RPS therapy pulses captured achamber. Also, analysis of such capturing stimuli can be used to monitorimprovement in a patient's contractility (presumably as a result of RPStherapy delivery and other palliative therapies).

FIG. 4 is a flow chart providing an overview of a method for monitoringcardiac contractility based on sensing LV lateral wall acceleration.Monitoring may be performed on an acute or chronic basis, using animplanted or external device in association with a LV lead equipped withan acceleration sensor as described above. Monitoring may be performedfor diagnostic, prognostic, or therapy evaluation purposes. Therefore,monitoring may be performed post-operatively, during drug infusion,subsequent to a medical or device-delivered therapy, or on a chronicbasis for ambulatory monitoring of patient status or therapyoptimization and evaluation,

Evaluation of LV contractility is of interest for both diagnostic andtherapeutic applications. Thus, it is recognized, that aspects of thepresent invention may be employed for cardiac monitoring purposes withor without optimization or evaluation of a therapy. As such, method 200summarized in FIG. 4 may be implemented in an implantable or externaldevice, such as the devices shown in FIGS. 1A, 1B and FIG. 3, formonitoring LV contractility by deriving and storing an index of cardiaccontractility based on an LV wall acceleration signal. The therapydelivery functions of such devices may be selectively disabled or, ifenabled, the RPS therapy optimization and contractility monitoring basedon LV acceleration may be selectively enabled or disabled such thatmonitoring function only are enabled. Method 200 may alternatively beimplemented in internal or external devices that do not include therapydelivery capabilities but, in association with an LV lead equipped withan acceleration sensor, are capable of processing and storing LVacceleration data.

Monitoring may be performed on a continuous, periodic or triggeredbasis. For example, LV function may be evaluated on a periodic basissuch as hourly, daily, weekly, or otherwise. Additionally oralternatively, LV function may be evaluated on a triggered basis, whichmay be a manual or automatic trigger. Automatic triggers may be designedto occur upon the detection of predetermined conditions during which LVfunction evaluation is desired, such as a particular heart rate range,activity, or other conditions.

Manual triggers for LV acceleration sensing and/or data storage may bedelivered by a clinician or by a patient, for example when the patientfeels symptomatic. Methods for manually triggering the storage ofphysiological data in an implantable device are generally described inU.S. Pat. No. 5,987,352 issued to Klein, et al., hereby incorporatedherein by reference in its entirety.

Method 200 begins at step 205 when monitoring is enabled according to aperiodic, continuous or triggered mode of operation. At step 210, a datacollection window is set. LV acceleration data is preferably collectedduring ventricular systole and most preferably during the isovolumiccontraction phase. In one embodiment, the data collection window is afixed time interval triggered by a sensed R-wave or a ventricular pacingpulse. The data collection window may begin immediately after, orfollowing a predefined interval after delivery of a first or subsequentRPS therapy pulse (herein a primary “P1” pacing pulse and/or additionalpulses denoted as “P2”) and preferably extending for a period of timethereafter.

FIG. 5 is a plot 500 of sample LV lateral wall acceleration data (LVA)502 and simultaneous hemodynamic and electrical data acquired during onecardiac cycle wherein a first evoked depolarization due to a firstpacing stimulus (P1) is followed by additional RPS therapy stimulus (P2)delivered within the refractory period (represented by dashed line 504).That is, the trace 508 appearing below the pacing stimulus trace 506represents a ventricular EGM signal showing a typical (evoked) QRScomplex of relatively large amplitude followed by a relatively smalleramplitude T-wave. The QRS complex marks the electrical activation of themyocardial tissue, causing depolarization and subsequent contraction ofthe myocardial fibers. The LVA trace 502 represents a nominalacceleration signal obtained from a motion sensor (e.g., anaccelerometer) placed to measure LV free wall acceleration. LVA is seento reach a peak shortly after the QRS complex arrives. The S1 phaseindicated on plot 500 corresponds to the isovolumic contraction phase ofventricular systole and is associated with the first heart sound (S1)which occurs at the beginning of systole. LV free wall accelerationduring this isovolumic phase, also referred to herein as “S1 phase”, isnot constant. In the example shown, LVA forms at least two distinct twopeaks, A₁ and A₂, during the S1 phase. Varying conditions may result inone, two, three or possibly more LVA peaks during the isovolumiccontraction phase. During isovolumic contraction, a large increase in LVpressure (LVP) denoted by reference numeral 512 is generated asillustrated in plot 500. LVP rises rapidly during the isovolumic phase(as illustrated by trace 510) which depicts an exemplary temporalderivative of LVP (dP/dt). As LVP reaches a peak, the aortic valveopens, initiating the systolic ejection phase and an associated increasein aortic flow (Ao FLOW) as illustrated by trace 514. After LVP falls,the aortic valve closes. During this phase, associated with the secondheart sound, S2, the LVA signal 502 exhibits one or more peaks that aretypically lower in amplitude than the S1 peaks.

While not depicted in FIG. 5, assuming undesirable capture due to the P2stimulus subsequent cardiac cycles will exhibit pronounced augmentationof pressure and flow typically characterized by two peak pressuresignals. Thus, such subsequent cycles can also be monitored to determineif a prior RPS pulse or pulses captured the heart. However, theacceleration signal due capture are readily discernible as thosedepicted in FIG. 5 due to the P1 pacing stimulus (e.g., A1, A2, etc.)although they will appear as a second series of peak motion signalsapproximately when the S2 heart sound would have been detected but forthe delivery of the extrasystolic stimulation.

Referring again to FIG. 4, method 200 senses the LV lateral wallacceleration signal at step 215 during the data collection window set atstep 210 such that it extends approximately from the start to the end ofthe isovolumic contraction phase. Preferably the acceleration sensor isimplanted in or proximate to the LV free wall as described above. Morepreferably, an LV acceleration signal is obtained from an accelerometerlocated on a coronary sinus lead or an epicardial lead positioned suchthat the accelerometer is situated over the mid-lateral, mid-basal orbasal segment of the left ventricular free wall. At step 215, the LVlateral wall acceleration signal is acquired over a number of cardiaccycles.

At step 225, the acceleration signal is determined and stored or alogical flag is set (e.g., non-capture confirmed, non-capture suspect,loss of capture). Additional information may be stored with the LVA datasuch as other sensed physiologic data and/or a time and date labeland/or other parametric information. When method 200 is executed by anexternal system, LVA data may be displayed in real-time or stored andpresented following a monitoring episode. When method is executed by animplanted device, LVA data may be stored for later uplinking to anexternal device for display and review by a physician. Such data couldinclude percent paced capture for the LV or the like.

As indicated previously, LV lateral wall acceleration may be monitoredfor both capture of a P1 pulse and confirmation of non-capture of the P2pacing pulse(s). FIG. 6 is a flow chart summarizing steps included in amethod for monitoring LV non-capture due to RPS delivery based on LVlateral wall acceleration. Method 300 begins at step 305 wherein atherapy is delivered or administered at nominal settings or dosages. Atherapy may be a single or dual chamber (and/or multi-site electrode)form of RPS therapy, a therapy for treating myocardial ischemia, amedical therapy, or any other known therapy for improving cardiaccontractility. As will be described, an iterative procedure may beperformed for determining the optimal settings for RPS delivery (e.g.,amplitude, number of pulses, polarity, pulse widths, intervals, etc.) ordosages at which a therapy should be delivered for ensuring LVnon-capture based on a measurement of LV free wall acceleration.

Depending on the type of therapy administered, an optional stabilizationperiod may be provided at step 310 to allow the hemodynamic response toa change in therapy to stabilize prior to monitoring LVA. Astabilization period may range from several seconds, to minutes, hoursor even days depending on the therapy being delivered.

At step 315 a data collection window is set, preferably extending justbeyond delivery of an LV pacing pulse. At step 320, the LVA signal issampled during the data collection window for each cardiac cycle duringa predetermined time interval and/or for a predetermined number ofcardiac cycles. In an alternative embodiment, the LVA signal may beacquired continuously during the predetermined time interval or numberof cardiac cycles and subsequently processed to separate componentsassociated with the isovolumic contraction phase, and more particularlywith the first acceleration peak during isovolumic contraction. The timeinterval or number of cardiac cycles preferably extends over at leastone respiration cycle such that averaging of the LVA signal over arespiration cycle may be performed to eliminate variations in the LVAmeasurements due to respiration. In one embodiment, the start and stopof LVA data acquisition may be triggered by sensing a respiration cycle.Respiration may be detected based on impedance measurements or othermethods known in the art.

At decision step 325, verification of a stable heart rate during thedata acquisition interval is performed. Heart rate instability, such asthe presence of ectopic heart beats or other irregularities, wouldproduce anomalous LV data. As such, the heart rate preferably stayswithin a specified range. In one embodiment, heart rate stability may beverified by determining the average and standard deviation of thecardiac cycle length during the data acquisition period. The cardiaccycle length is determined as the interval between consecutiveventricular events including ventricular pacing pulses and any sensedR-waves. If the average cardiac cycle length or its standard deviationfalls outside a predefined range, the data is considered unreliable.Data acquisition may be repeated by returning to step 315 until reliabledata is collected for the current therapy settings.

At step 330, signal averaging is performed to minimize the effects ofrespiration-related or other noise. The signals acquired during eachcardiac cycle over the data collection interval are averaged to obtainan overall average LVA signal. At step 335, one or more signal featuresare determined from the averaged LVA signal as an indication ofnon-capture of a ventricle due to RPS therapy delivery (e.g.,non-capture of a series of maximum acceleration signals following pacingdelivery—P1 or P2) at the nominal or modified therapy settings andstored in device memory with corresponding physiologic information.

If all therapy settings need to be adjusted or a regime of nominaltesting signals have yet to be applied, as determined at decision step340, the method 300 adjusts the therapy at step 345 and returns tooptional step 310 and repeats steps 315 through 335 to determine, basedupon the LVA signals whether non-capture of the ventricle has occurreddue to the P2 RPS stimulation. Once all test settings have been applied,the optimal setting is identified based on the stored LVA data at step350.

FIG. 7 is a flow chart summarizing steps included in a method fordetermining LV chamber non-capture based on LV acceleration. At step405, the A-V interval is programmed to a previously determined optimalor nominal setting. An A-V interval optimization procedure may beperformed prior to delivering PESP therapy. The A-V interval may beoptimized based on methods known in the art. For example, an A-Vinterval may be selected as the shortest A-V interval that does nottruncate ventricular filling based on echocardiographic evaluation.Alternatively, an optimal A-V interval may be selected based on RVapical motion as detected by an accelerometer placed at the RV apex. TheA-V interval may alternatively be set to a nominal setting at step 405.

At step 410, as applicable a V-V interval is set to a test interval. Arange of test intervals are predefined and may be delivered in a random,generally increasing, or generally decreasing fashion. A range of testintervals may include intervals that result in the right ventricle beingpaced prior to the left ventricle and intervals that result in the leftventricle being paced prior to the right ventricle and simultaneousright and left ventricular pacing. A set of exemplary test intervalsincludes right ventricular pacing 20 ms and 40 ms prior to LV pacing,simultaneous LV and RV pacing (a V-V interval of 0 ms), and LV pacing 20ms and 40 ms prior to the RV.

Method 400 proceeds to determine whether ventricular capture isoccurring due to the P2 pacing stimulation. A data collection window isset at step 415, and LVA data is collected for a predetermined timeinterval or number of cardiac cycles at step 420 during the datacollection window applied to each cardiac cycle. After verifying astable heart rate at step 425, signal averaging is performed at step 430allowing an average peak amplitude or average peak-to-peak difference ofthe first acceleration peak (A₁) during the period of time when LVcapture would be expected to occur and method 400 returns to step 410 tocontinue monitoring for LV non-capture in a temporal window subsequentto the P1 capturing pulse and for all or a portion of the refractoryperiod of the chamber (e.g., periodically, continuously oraperiodically)

When method 400 is executed by an external pacing system, LVA data isavailable for real-time display or stored and presented followingcapture confirmation. An attending clinician may program the LV pacingthresholds or the external system may adjust the thresholds to confirmLV capture due to P1 stimulus and desirable LV non-capture due to RPStherapy delivery. When method 400 for identifying LV capture thresholdsis executed by an implanted device, LVA data may be processed and storedfor later uplinking to an external device for display and review by aphysician. The implanted device can automatically adjust the pacingpulse parameters (e.g., amplitude, duration, polarity, etc.).

Thus a method and apparatus have been described for monitoring LVchamber capture and/or optimizing threshold to ensure LV non-capture(automatically or manually) and/or changes in contractility based on LVlateral wall acceleration measured using a LV lead equipped with anacceleration sensor. The methods described herein may advantageously beapplied in numerous cardiac monitoring or therapy modalities includingchronic or acute applications associated with implantable or externaldevices.

As is known in the art, besides the transducers described hereinabove,other types of transducers may be used provided, in general, that suchtransducers are hermetically sealed, are fabricated (on least on theexterior surfaces) of substantially biocompatible materials andappropriately dimensioned for a given application. With respect toappropriate dimension, a transducer intended to transvenous deploymentshould be susceptible of catheter or over-the-wire delivery. Thus, theradial dimension should be on the order of less than about 11 French andpreferably about less than eight French. Also, the transducer should besomewhat supple, and not too long, in the longitudinal dimension so thatthe transducer can safely navigate the venous system, pass through thecoronary sinus and enter vessels branching from the coronary sinus(e.g., the great cardiac vein, and the like). These dimensions can berelaxed for a transducer intended for deployment though a portion of thechest (e.g., a thoracotomy) with an affixation mechanism adapted tomechanically couple adjacent the lateral wall. Two adjacent locationsinclude the epicardium and the pericardium. The dimensions may berelaxed to a greater extent if the epicardial receives the transducer,and to a lesser extent, to a portion of the pericardium. As is wellknown, the pericardium is the membranous sac filled with serous fluidthat encloses the heart and the roots of the aorta and other large bloodvessels. One example of appropriate fixation apparatus for epicedialapplication is a helical tipped lead that is screwed into the surface ofthe epicardium. For pericardial fixation a sealing member (e.g.,compressible gasket or opposing members on each side of the pericardialsac) may be used in addition to an active fixation member such as ahelical tipped lead.

As is also known in the art related to sensors and transducers,accelerometers can be described as two transducers, a primary transducer(typically a single-degree-of-freedom vibrating mass which converts theacceleration into a displacement), and a secondary transducer thatconverts the displacement (of a seismic mass) into an electric signal.Most accelerometers use a piezoelectric element as a secondarytransducer. Piezoelectric devices, when subjected to a strain, output avoltage proportional to the strain, although piezoelectric elementscannot provide a signal under static (e.g., constant acceleration)conditions. Important characteristics of accelerometers include range ofacceleration, frequency response, transverse sensitivity (i.e.sensitivity to motion in the non-active direction), mounting errors,temperature and acoustic noise sensitivity, and mass.

One type of primary transducer, which describe the internal mechanism ofthe accelerometer, include spring-retained seismic mass. In mostaccelerometers, acceleration forces a damped seismic mass that isrestrained by a spring, so that it moves relative to the casing along asingle axis. The secondary transducer then responds to the displacementand/or force associated with the seismic mass. The displacement of themass and the extension of the spring are proportional to theacceleration only when the oscillation is below the natural frequency.Another accelerometer type uses a double-cantilever beam as a primarytransducer which can be modeled as a spring-mass-dashpot, only theseismic mass primary transducer will be discussed.

Types of secondary transducers, which describe how the electric signalis generated from mechanical displacement, include: piezoelectric,potentiometric, reluctive, servo, strain gauge, capacitive, vibratingelement, etc. These are briefly described as an introduction for theuninitiated.

Piezoelectric transducers are often used in vibration-sensingaccelerometers, and sometimes in shock-sensing devices. Thepiezoelectric crystals (e.g., often quartz or ceramic) produce anelectric charge when a force is exerted by the seismic mass under someacceleration. The quartz plates (two or more) are preloaded so that apositive or negative change in the applied force on the crystals resultsin a change in the electric charge. Although the sensitivity ofpiezoelectric accelerometers is relatively low compared with other typesof accelerometers, they have the highest range (up to 100,000 g's) andfrequency response (over 20 kHz).

Potentiometric accelerometers utilize the displacement of thespring-mass system linked mechanically to a wiper arm, which moves alonga potentiometer. The system can use gas, viscous, magnetic-fluid, ormagnetic damping to minimize acoustic noise caused by contact resistanceof the wiper arm. Potentiometric accelerometers typically have afrequency range from zero to 20-60 Hz, depending on the stiffness of thespring, and have a high-level output signal. They also have a lowerfrequency response than most other accelerometers, usually between 15-30Hz.

Reluctive accelerometers use an inductance bridge, similar to that of alinear variable differential transducer to produce an output voltageproportional to the movement of the seismic mass. The displacement ofthe seismic mass in inductance-bridge accelerometers causes theinductances of two coils to vary in opposing directions. The coils actas two arms of an inductance bridge, with resistors as the other twoarms. The AC output voltage of the bridge varies with appliedacceleration. A demodulator can be used to convert the AC signal to DC.An oscillator can be used to generate the required AC current when a DCpower supply is used, as long as the frequency of the AC signal is fargreater than that of the frequency of the acceleration.

In servo accelerometers, acceleration causes a seismic mass “pendulum”to move. When motion is detected by a position-sensing device, a signalis produced that acts as the error signal in the closed-loop servosystem. After the signal has been demodulated and amplified to removethe steady-state component, the signal is passed through a passivedamping network and is applied to a torquing coil located at the axis ofrotation of the mass. The torque developed by the torquing coil isproportional to the current applied, and counteracts the torque actingon the seismic mass due to the acceleration, preventing further motionof the mass. Therefore, the current through the torquing coil isproportional to acceleration. This device can also be used to measureangular acceleration as long as the seismic mass is balanced. Servoaccelerometers provide high accuracy and a high-level output at arelatively high cost, and can be used for very low measuring ranges(well below 1 g).

Strain gauge accelerometers, often called “piezoresistive”accelerometers, use strain gauges acting as arms of a Wheatstone bridgeto convert mechanical strain to a DC output voltage. The gauges areeither mounted to the spring, or between the seismic mass and thestationary frame. The strain gauge windings contribute to the springaction and are stressed (i.e., two in tension, two in compression), anda DC output voltage is generated by the four arms of the bridge that isproportional to the applied acceleration.

These accelerometers can be made more sensitive with the use ofsemiconductor gauges and stiffer springs, yielding higher frequencyresponse and output signal amplitude. Unlike other types ofaccelerometers, strain gauge accelerometers respond to steady-stateaccelerations.

In a capacitive accelerometer a change in acceleration causes a changein the space between the moving and fixed electrodes of a capacitiveaccelerometer. The moving electrode is typically a diaphragm-supportedseismic mass or a flexure-supported, disk-shaped seismic mass. Theelement can act as the capacitor in the LC or RC portion of anoscillator circuit. The resulting output frequency is proportional tothe applied acceleration.

In a vibrating element accelerometer, a very small displacement of theseismic mass varies the tension of a tungsten wire in a permanentmagnetic field. A current through the wire in the presence of themagnetic field causes the wire to vibrate at its resonant frequency(like a guitar string). The circuitry then outputs a frequencymodulation (deviation from a center frequency) that is proportional tothe applied acceleration. Although the precision of such a device ishigh, it is quite sensitive to temperature variations and is relativelyexpensive.

Thus, those of skill in the art will recognize that while the presentinvention has been described herein in the context of specificembodiments, it is recognized that numerous variations of theseembodiments may be employed without departing from the scope of thepresent invention. The descriptions provided herein are thus intended tobe exemplary, not limiting, with regard to the following claims.

1. A method for assessing ventricular chamber status following deliveryof a refractory period stimulation (RPS) therapy, comprising: sensingcontraction of a portion of a ventricular chamber of a heart during atleast part of the refractory period of the chamber during delivery of arefractory period stimulation (RPS) therapy with a deployed movementtransducer and for measuring a signal from the transducer related to thesensed movement; coupling said signal to a means for detecting thesensed movement during said refractory period of the chamber, whereinthe RPS therapy comprises at least one pulse and is delivered duringsaid refractory period of said chamber; filtering the signal obtainedduring the period of time; and one of determining, storing, andprogramming a logical flag relating to whether or not the ventricularchamber was captured by the RPS therapy.
 2. A method for determining theconfiguration, sequence, waveform, polarity, duration, or timing fordelivering left ventricular (LV) electrical pulses and measuring theincidence of mechanical capture and non-capture events due to pacingtherapy delivery and refractory period stimulation (RPS) therapydelivery during a given cardiac cycle, comprising: disposing atransducer that is adapted to directly sense movement of a portion of aLV chamber of a heart and providing a signal related to the movement;coupling said signal to a means for detecting the movement during atleast a part of the refractory period of the LV chamber subsequent todelivery of at least one refractory period stimulation pulse; and one ofdetermining, storing, and programming a logical flag relating to whetheror not the LV chamber contracted due to delivery of the at least onerefractory period stimulation pulse.
 3. A method according to claim 2,wherein said transducer is adapted to be disposed in a portion of one ofthe coronary sinus vessel and a blood vessel fluidly coupled to saidcoronary sinus.
 4. A method according to claim 3, wherein saidtransducer comprises an accelerometer.
 5. A method according to claim 4,wherein the accelerometer comprises a uniaxial accelerometer having alongitudinal sensing axis substantially aligned toward the leftventricular apex portion of the heart.
 6. A method according to claim 3,wherein said transducer comprises a biaxial accelerometer.
 7. A methodaccording to claim 3, wherein said transducer comprises a triaxialaccelerometer.
 8. A method according to claim 2, wherein said transduceris adapted to be disposed adjacent to a portion of the epicardium of theleft ventricle of the heart.
 9. A method according to claim 8, whereinthe portion of the epicardium is a portion of the lateral wall of theleft ventricle.
 10. A method according to claim 9, wherein the portionof the lateral wall is a basal portion of the lateral wall.
 11. A methodaccording to claim 10, wherein the portion of the lateral wall is amid-basal portion of the lateral wall.
 12. A method according to claim2, wherein said transducer is adapted to be disposed within thepericardium of the heart.
 13. A method according to claim 4, wherein thedevice comprises an implantable medical device.
 14. A method accordingto claim 13, wherein the first pacing electrode or the second pacingelectrode further comprises a sense electrode in electricalcommunication with a sensing circuit coupled to the device.
 15. Acomputer readable medium programmed with instructions for determiningthe configuration, sequence, waveform, polarity, duration, or timing fordelivering left ventricular (LV) electrical pulses and measuring theincidence of mechanical capture events during the refractory period fora given cardiac cycle, comprising: instructions for sensing movement ofa portion of a LV chamber of a heart and providing a signal related tothe movement; instructions for coupling said signal to a means fordetecting the movement during at least a part of the refractory periodof the LV chamber subsequent to delivery of at least one refractoryperiod stimulation pulse; and instructions for one of determining,storing, and programming a logical flag relating to whether or not theLV chamber contracted due to delivery of the at least one refractoryperiod stimulation pulse.
 16. A computer readable medium according toclaim 15, wherein said transducer is adapted to be disposed in a portionof the coronary sinus vessel or a blood vessel fluidly coupled to saidcoronary sinus.
 17. A computer readable medium according to claim 16,wherein said transducer comprises an accelerometer.
 18. A computerreadable medium according to claim 17, wherein the accelerometercomprises a uniaxial accelerometer having a longitudinal sensing axissubstantially aligned toward the left ventricular apex portion of theheart.
 19. An apparatus for confirming capture of a left ventricular(LV) chamber due to LV pacing stimulus delivery and confirmingnon-capture due to delivery of refractory period stimulation (RPS)therapy, comprising: transducer means for measuring movement of aportion of the lateral wall of a LV chamber and providing a movementsignal related to such movement; a movement measurement circuitoperatively coupled to the transducer means; a pulse generator coupledto the measurement circuit; a left pacing electrode in electricalcommunication with a portion of the LV chamber and electrically coupledto a RPS therapy delivery circuit of the pulse generator; and an LVchamber movement threshold circuit coupled to the movement signal andadapted to generate a signal relating to one of a capture, non-captureand relative contractility status of the LV chamber.
 20. An apparatusaccording to claim 19, wherein the pulse generator comprises animplantable pulse generator.